Various conventional methods exist for connecting a contact and an electric wire. One such method connects the electric wire and the contact by pressure welding. The pressure welding method is used for connecting an electric wire having a core wire sheathed with a sheathing member to a sharp piercing member of a contact.
For example, Japanese Patent Publication No. 56-30955 teaches a contact that has a piercing member with a sharp end. The piercing member has a pair of press-fitting sections that expand upward and open outward. When an electric wire is connected to the contact, the sharp end of the piercing member pierces a sheathing member of the electric wire such that a core wire of the electric wire and the piercing member are brought into contact with each other. The press-fitting sections maintain the contact of the core wire and the piercing member by bending along an outer periphery of the sheathing member so as to cover the outer periphery of the sheathing member after the piercing member is brought into contact with the core wire. In a case where the core wire is formed by combining a plurality of wires, however, when the piercing member pierces into the electric wire, the external piercing force deforms the electric wire causing the plural wires to spread-out in the sheathing member. Because the press-fitting sections are subject to plastic deformation over a long period of time, the press-fitting sections may not be able to keep all the wires of the core in contact with the piercing member.
In an effort to solve this problem, Japanese Patent Laid-Open No. 61-133584 teaches an electrical connector with a means for preventing an electric wire from being deformed when a piercing member pierces into the electric wire. The electrical connector includes a contact having a sharp piercing member and a cover housing with a holding section that retains a circumferential surface of the electric wire. The holding section is made of a rigid resin material. Since the sheathing member of the electric wire is elastic, the sheathing member allows the electric wire to be firmly held by the holding section when a connection is made, thereby, preventing the deformation of the electric wire. The elasticity of the sheathing member of the electric wire, however, is prone to dissipate by secular changes after the connection is made. Once the elasticity of the sheathing member is dissipated, the electric wire moves relative to the piercing member, reducing the reliability of the electrical connection between the core wire and the piercing member.
In another example, Japanese Patent Laid-Open No. 2002-175845 teaches an electrical connector that has a terminal block including a plurality of electric wires laterally arranged in a line according to contacts laterally arranged in a predetermined pitch. U-shaped elastic members are arranged in the terminal block according to the array pitch of the plural electric wires. Opposing portions of the U-shaped elastic members flank the sides of the electric wires. The opposing portions are urged toward each other, to hold the respective electric wire therebetween. A piercing member of the contact pierces into the electric wire from below to make a connection therewith. The U-shaped elastic members prevent the electric wires from being deformed when the connection is made. The U-shaped elastic members also prevent movement of the electric wire relative to the piercing member, even when a sheathing member of the electric wire loses elasticity due to secular changes. When the electrical connector, however, is used with electric wires having a large-diameter without changing the array pitch of the contacts, the space between adjacent electric wires is reduced, thereby, eliminating the space needed to arrange the U-shaped elastic members in the terminal block. As a result, cracking may occur during formation of the terminal block.